The invention relates to a hydraulic power transmission device.
In a conventional automatic transmission, torque generated by an engine is transmitted to the transmission via a torque converter as a hydraulic power transmission device. Gear shifting is performed in the transmission, and the torque is transmitted to a drive shaft. The torque converter has a case, which consists of a front cover, rear cover, etc., plus a pump impeller, a turbine runner, a stator, a one-way clutch, a lock-up device, a damper device, etc. The torque converter transmits torque via oil circulating in its interior and acts as a torque conversion device or a fluid coupling.
More specifically, rotation that is transmitted from the engine via the crankshaft is transmitted to the pump impeller via the front cover and the rear cover. When the pump impeller rotates, the oil inside the torque converter circulates by centrifugal force among the pump impeller, the turbine runner, and the stator, causing the turbine runner to rotate. The turbine runner is coupled to the transmission input shaft such that the output from the torque converter is transmitted to the transmission. The stator is positioned between the pump impeller and the turbine runner, and when there is a large difference in the rotation speeds of the pump impeller and the turbine runner, the stator converts the oil flow to a direction that assists the rotation of the pump impeller, thereby increasing the torque.
In the torque converter, the lock-up device is provided to prevent energy loss due to oil slippage. When the vehicle speed reaches a prescribed value, the lock-up device mechanically couples the front cover and the turbine runner. The rotation that is transmitted from the engine is therefore transmitted to the input shaft via the front cover and the lock-up device, preventing energy loss due to oil slippage. (See, for example, the published Japanese translation of PCT international application No. 2001-514366.)
However, in a conventional torque converter, the positioning of the lock-up device adjacent to the turbine runner increases the length of the torque converter in the axial direction, making the torque converter larger.